The use of smooth or partly textured weft yarns, particularly synthetic filament weft yarns in looms with a pneumatic weft insertion has posed a problem because these relatively smooth filament threads have a tendency to cause faulty weft insertions into a loom shed, especially into a pneumatic weaving loom in which the weft threads are transported through a weft insertion channel extending through the loom shed, by a main insertion nozzle and a plurality of relay nozzles. This problem is relatively small or nonexistent where such smooth or partially textured weft threads are used in a gripper loom or in a projectile weaving loom in which the transfer of the weft thread takes place mechanically. Thus, in such a mechanical transfer it is irrelevant whether the filament threads are completely partly or not at all texturized. However, it appears that a texturized thread is even preferred in gripper looms compared to smooth filament threads.
In connection with the use of synthetic filament weft yarns as weft threads in pneumatic looms, the degree of texturizing of the initially smooth yarns is of substantial importance because the thread surface characteristers determines the probability of faulty weft insertions. It is generally known that synthetic filament weft threads available on the market must be treated in a certain texturizing or entangling operation prior to using these threads in a pneumatic weft insertion loom in order to prevent individual filaments from popping out of the thread. However, conventional thread texturizing operations outside a loom achieve a weft thread texture that does not take into account the conditions that must be met for using such filament yarns in a pneumatic weft insertion loom. Practical experience has shown that conventional texturizing outside the loom results in yarns which do not meet ideal air insertion requirements because the texturizing does not take into account the conditions that must be satisfied when these yarns are to be used as weft threads in pneumatic weft insertion looms. For example, conventionally texturized weft threads are not contemuously texturizing along the entire thread length. Actually, conventionally texturized filament threads have only texturized points which are relatively widely spaced from one another along the length of the filament weft thread. The purpose of such texturized points is primarily to avoid an untwisting of the filaments in a filament thread such texturized points do not prevent individual filaments from becoming loose between texturized points.
Such conventionally texturized weft threads with widely spaced texturized points are only marginally or not at all suitable for use as weft threads in a pneumatic weft insertion loom because the formation of so-called blown-out weft threads that mar the fabric appearance and frequently require the removal of a blown-out thread cannot be avoided. By a blown-out thread is meant a weft thread that, due to the pneumatic insertion into the shed, has been untwisted at least partly by the weft insertion jets, whereby individual filaments pop out of the body of the filament thread. This blow-out takes place primarily when the main insertion jet or any of the relay jets impacts on the weft thread along a section outside a texturized point. Such thread sections can be relatively long between two texturized points in the same conventional filament weft thread. The term "texturizing" as used herein includes initial texturizing where the weft thread is smooth and further or post-texturizing where the weft thread is already provided with an initial texturizing.